Tin plating, intended for engineering purposes, is used for corrosion protection to facilitate soldering, to improve anti-galling characteristics and as a stop-off barrier in the nitriding of high-strength steels.
Note: Some corrosion may be expected from tin coatings exposed outdoors. In normal indoor exposure, tin is protective on iron, steel, copper and copper alloys.
Specification: MIL-T-10727 Tin Plating: Electrodeposited or Hot-Dipped.
- Type I: Electrodeposited. Reference ASTM B-545 Standard Specification for Electrodeposited Coatings of Tin
- Type II: Hot-Dipped
Tin should be not less than 99.5% except where deliberately alloyed for special purposes. The Code position of lead, bismuth, antimony, copper or nickel with the tin reduces the risk of whisker growth (Metal filaments, or whiskers, sometimes grow spontaneously from the surface of electrodeposited metals such as tin, cadmium, and zinc within a period that may vary from weeks or months to years). These whiskers are about 0.0001" (2.5µm) in diameter, can grow up to 3/8" 10mm) long and can have a current carrying capacity of as much as 10 mA. A tin-lead plating that is extensively used for the prevention of whiskering has a nominal lead composition of 7% (with allowed variations of ±5%) b mass, the balance being tin.
Coatings may be matte, bright or flow brightened. Matte coatings are obtained by adding proprietary brightening agents to the plating bath. Flow-brightened coatings are obtained by heating the matte coating above the melting point of tin for a few seconds followed by quenching.
Thickness as specified on drawing. Color is gray-white in a plated condition. Has very high luster in fused condition. Soft and very ductile. Corrosion resistance good. When specified, coated items should meet 24-hour 5% salt-spray requirement. Solderability is excellent. Tin is not good for low temperature applications changes structure and loses adhesion when exposed to temperatures below -40°C). If bright finish is desired specify Bright Tin plate to be used in lieu of fused tin. Thickness can exceed that of fused tin and thicker deposits show excellent corrosion resistance and solderability.
(.0001- .0023" thickness) Flash for soldering.
(.0002-.0004" thickness) To prevent galling and seizing.
(.0003" min. thickness) Where corrosion resistance is important.
(.0002-.0006" thickness) To prevent formation of case during nitriding.